This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below, after the main part of the detailed description section.
In current active antenna calibration systems, the hardware circuits are providing access to all TRX ports simultaneously to allow phase difference measurement of the signals. Wilkinson-divider-based signal parallel coupling is used in some cases of TDD systems when the horizontal TRX ports are suitably close to each other and there is space for parallel combining parts. The Wilkinson divider (also called a Wilkinson power divider) is a well-known form of power splitter/power combiner that is often used in microwave applications. It uses quarter wave transformers, which are easily fabricated as quarter wave lines on printed circuit boards and as a result it offers the possibility of proving an inexpensive and simple splitter/divider/combiner while still providing high levels of performance. In multi-TRX constructions of, e.g., 3D beamforming and 5G, a serial bi-directional couplerline can be used instead, or multiple couplerlines can be, e.g., connected in parallel with Wilkinson dividers or switched, and the couplerline/couplerlines are measured from both ends of the line to eliminate the serial couplerline distance propagation effect between the coupling positions.
In the highest frequency AAS/5G implementations, there will be IF design and beamforming is made either by radiation element HW directly or with analogue/hybrid beamforming with phase adjustment blocks inside the high end frequency TRX sub groups. For this purpose, a high RF frequency sub group calibration can be used in addition to a whole system calibration to minimize the number of connections which need to be visible to/from the whole system calibration level.
Although current active antenna calibration systems are able to perform antenna calibrations, these systems could be improved.